Hearing aid



FIG. 1 is a top perspective view of the hearing aid;

FIG. 2 is a front side view thereof;

FIG. 3 is a rear side view thereof;

FIG. 4 is a right side view thereof;

FIG. 5 is a left side view thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom thereof.

The broken lines in the drawings depict portions of the article that form no part of the claimed design. 

CLAIM The ornamental design for a hearing aid, as shown and described. 